Drywall has become a dominant material in the production of interior building partitions. In particular, interior building partitions generally comprise a vertical stud wall which is used as a support for pre-formed drywall panels that are attached to the stud wall. Joints between adjacent panels of drywall are usually taped, and finished with joint or drywall compound. One type of apparatus or tool for applying joint compound is disclosed in U.S. Pat. No. 2,815,142 issued Dec. 3, 1957. This apparatus mechanically applies tape and joint compound contemporaneously. After the tape and the first coat of joint compound has been applied over the joint, it is typical to apply multiple coats of joint compound. The multiple coats are typically applied using finishing tools such as a corner head, a coater, a flat box or other box tool.
A traditional box tool is constructed with a slotted orifice in the bottom surface which acts as an outlet through which the drywall compound is dispensed as well as refilled. A movable pressure plate on the box tool has springs attached to bias it to an open position. A handle pivotably affixed to the pressure plate allows an operator to apply inward pressure to the pressure plate to force drywall in the box tool through the outlet slot and onto a joint or the like. The expelled drywall compound is then spread and smoothed by a blade-like projection on the box tool as the box tool is moved along a joint. A cable is controlled by a brake lever on the handle to selectively lock the box tool on the handle and prevent relative pivotal motion thereof. One glaring inefficiency associated with use of traditional box tools in finishing is the frequent requirement of refilling the relatively small box tool which requires a lot of additional time and is labor intensive adding to the cost of the job.
More recently, box tools have been supplied with a source of pressurized drywall which is continuously fed by a supply line into and through the handle from a pump supply device for dispersion into the box tool so as to make the dispensing system more efficient and eliminate the costly downtime problem noted above. One known finishing tool system includes a handle equipped with a brake lever as well as an on/off switch and a volumetric control to regulate the continuous flow of pressurized drywall compound to the box tool. This system allows an operator to continuously feed drywall compound to the box tool and simultaneously control locking the box tool. However, this system is not designed to provide a separate optional manual control to vary the flow of pressurized drywall compound. In addition, such system does not provide relief valve protection in the event of excessive pressure buildup of drywall compound. The absence of these features detracts from the productivity, usefulness and ease of operating the box tool dispenser.
Accordingly, it is desirable to provide a system for applying drywall compound to wallboard joints with an improved control arrangement which will overcome the deficiencies of the prior art and enhance the operability, speed, efficiency and versatility of a drywall finishing operation.